In a high-speed optical network system, an optical multiplexing transmission technology in which optical signals of a plurality of channels are multiplexed by using one fiber is often used. In an existing optical multiplexing transmission technology, a main multiplexing technology includes time division multiplexing (TDM), wavelength division multiplexing (WDM), frequency division multiplexing (FDM), orthogonal frequency division multiplexing (OFDM), or code division multiplexing (CDM). In the foregoing multiplexing technology, the CDM can multiplex a plurality of signals in one timeslot and one wavelength, providing a high degree of multiplexing. Coherent Code Division Multiple Access (CDMA) is an important implementation in an optical communications multipoint-to-point system. A coherent CDMA system is compatible with an existing commercial coherent component. In a network architecture based on coherent CDMA, service sites send corresponding data on a same wavelength resource by using respective spreading codes. The spreading codes used by the service sites are mutually orthogonal. This ensures that a coherent receiver at a backbone node can recover data of the service sites by using different spreading codes. Therefore, the coherent receiver at the backbone node needs to use a corresponding digital signal processing (DSP) receiving method.
However, a current DSP architecture of the coherent receiver is only applicable to a point to point transmission system, and is not applicable to a coherent CDMA multipoint-to-point system. Moreover, due to a difference between transmission channels, a CDMA architecture in wireless communication cannot be completely applicable to an optical communications system either. In addition, in the coherent CDMA optical communications system, a transmission signal used by each user is a dual-polarization signal. Because a transmission channel is a fiber, effects such as polarization mode dispersion (PMD) and differential group delay (DGD) are caused, thereby affecting a CDMA signal.